Delta Connection for Start Big Motor

Not necessarily, though the starting current may be too much for the upstream supply system to cope with.

Starting big motors in Δ and direct-on-line requires an awful lot of power. Better, if it can be done, is to start them in * and switch to Δ when they are at, or nearly at, running speed.

Most of the induction motors nowadays, are selectable to be connected or started with star connection or Delta Connection. This is because that the common voltage that we have through out the country, like example, 220V and 415V of course with the variation of + 10% and the usage of these common voltage influence the manufacture to produce these two type of connection for the motors.

There is not much different between the starting current of Star connection or the Delta Connection motors. Both motor starting current, if you start it with the "Direct On Line" starter, will experience 7.5 time of the nominal running current of the induction motor.

Either, you start with star connection or delta connection, both type of connection have some minor effect to the motor, including the motor winding, bearing, the rotor and of course, the load that connected to the motor.

In order to avoid these effect that will cause damages to the motor and the connected load to breakdown, that why, the Star-Delta Starter is developed to restrict the starting current of these big induction motor. Starting big induction motor with Direct On Line or direct start, will cause sudden starting with high torque and the motor winding will experience high inrush of current and to your load it will experience of high starting torque.

Not only the effect is to the motor but direct delta starting of the big induction motor will also cause the secondary effect to your electrical system, where the sudden inrush current is diverted to this motor. Other load that connected to the electrical system will experience voltage drop and sequentially, the other load will trip off and causing necessary downtime to the plant.

For starting of big motors it is important to limit the current as starting current is very high in order to limit the load on the distribution system.So star delta connectors are normally used.In our power plant motors below 250KW are delta connected while motors above 250KW are star connected.So if your system is stable then its OK but is your distribution system in weak then it is necessary to use star delta starters or connect the motor in star permanently to avoid voltage drop as the motor starts.

can you tell me sir how the star-delta starter works.

Basically, the star-delta starters use 3 contactors to start the induction motor. Of course your induction motor must have 6 motor lead coming out from your motor winding.

The 3 contactor are called the "Main Contactor", the "Star Contactor" and the "Delta Contactor". The main contactor that is the R, Y, B will be directly connected to your main motor lead of U1, V1 and W1 wherealse, the other motor lead of U2, V2 and W2 will be connected to your delta contactor.

For the star contactor, the star point of the motor will be at the top of the star contactor and the bottom of the star contactor will be parallel with the delta contactor.

During starting, the Star Delta starter, will star point the motor terminal by the star contactor then the main contactor will energize to start the induction motor in star point.

After running for a while, when the timer is up, the Star contactor will de-energize and the Delta contactor will come in. The main contactor remain energize all the time.

So, you have your motor start with Star point and then Delta Point. That what it is call Star Delta Starters.

how the star-delta starter works - Search (bing.com)

what is big motor? you have to clarify.Is it interms of rating in KW then What is it u have in mind?For ur all MV motors of ratings 150 kw and above are always star connected.Delta or star has no relevence to starting current.

our induction motor is P=3.1MW,V(line)=3.3kv,starter=Delta(direct)???

The motor will be star connected.Pl check name plate.You can go in for DOL starting with a vacuum contactor or depending upon the load inertia (whether Soft load like pump) u can go in for a soft starter.One more thing a starter does not reduce starting current but the duration for which it persists except in the case of soft starters where voltage is smoothly raised.

Normally, you can also use reactor starter to start your 3.1MW motor at 3.3KV voltage.

Hey Folks,

A Wye Delta starter is a great way to limit the starting currents of a large motor. But now there are options. I have used soft starters with current limiting capabilities configured in Delta full time. Of course, when the current limiting was not enabled on this soft starter.. we were standing in the dark a few times. Read the manual.. lol.

This particulat soft starter, for what it is worth was a product from SAF Drives out of Kitchener Ontario called an OPAL. SAF is now called Brock Solutions.

Cheers.

Pl be aware a starter only limits duration for which starting current persist except in case of those where voltage is raised smoothly .There also at the min starting volktage a high current will be there and it will continue to rise till rated speed is reached.Wye Delta starters are used only in LV motors.3.1 Mw motor under ref will be either 3.3 kv or 6.6 or 11 KV whre dol is the best method alternatively the present rend is to go for soft starter.

how star connection can bear more current then delta.plz explain in detail,,,,,,all mechanism

It doesn't. It starts with less <...current then delta...> instead. Otherwise there would be no need for it.

You have not mentioned the Rating of Motor.Normally motors in Frame IEC 355 and above are in star connection particulary the motors of MV voltage like 3,3kv, to 11KV.Starting current duration is what matters which in turn depends on the load inertia.Higher it is more time it takes for the motor to raech rated rpm and starting current duration and hence heating is more .Large motors 400 KW and above are always in star connection. It is always the duration of starting current that matters